Photo-electric cell



June 23, 1931.

R. K. POTTER ,PHOTO ELECTRIC CELL Filed Sept. 8 92 rllll um. L

V INVEN 10 IRIZ0tJeI L v \.J H M W W AZ v Q ATTORNEY Patented June 23, 1931 UNITED PATENT .o- F-lic me]; 1:. urma, ornnwyonx, .n; .Y'., Assrsuoa TO AMERICAN rnnnrnonn nnn gmm m amcomm A-CORPQRAIION on NEW YORK BHOTO-ELECTRIC oELi.

Application filed SeptemberS, 1925. Serial No. 134,298;

This invention relates to photo-electric cells, and more; particularly to photo-electric cells having a; photo-sensitive cathode, .an

anode, a source of oltage connected between theelectrode terminals, and a gas content allowing ionization by collision.

In the usual form of photoelectric cell of this type tl e output ofthe cell ispropor- V tional to the quantity or intensityof theincidentlight. It is'the object of this invention to provide a satisfactory v photo-electric cell which is responsive not only to ariation in the quantity of the'li'ght but also to the dis 7 placement of a njincident'liglit beam of con- '5stant,or varyingintensity. .Such a cell is adyantageous; especially in certain reproduction methods. in which it obviates the neces sity of inclu ding special optical means as a part of the device." 6 In general the-cell embodying my invention issolari'anged that thejacclerating field overthe region between the sensitive area of theL ath deandthe anode is graduated; the w m a'gnituc le of the effective accelerating field being different for different positions of the light-beam. i i

If the accelerating field between the electrodes of a pl 1oto-electric cell issufiicient to I remoyeallpf the elections as fast ast-heyare relea'sed from the cathode'b y an incident light beamfand if there is no gas present in the cellenv'elope the output will depend solely upon the quantity of light. There will be no change in the output current with an increase srf'of the anode potential; If, howeven'gas is present in the tube, the output is no longer a simple function ofi the quantity of incident light but depends upon the kind; of gas, its pressure and temperature,the electrode spac- 4o"ing and the strength of the accele'ratingfield. The electrons released by the photo-electric action cause ionization of the gas if the mean free path of the gas molecules is shorter than" the path between the electrodes and if the electron a sufficient velocity before it strikes. In familiar types of cell'many' collisions take place in the distance between the cathode and the anode. Since ,each collision releases 59 more electrons, the action is cumulative.

Thetotal output current of a photo electr-ic cell of such type may be represented. the following relation: 1 i

in which 2' is the current due to photo ele'ctricelfect alone,

detailed description of the severalforms'jis read with reference to the accompanying drawings. Figures 1 and 2 are longitudinal and sectional Viewsillustrating the general principles of construction of'a photo-electric cell; Fig. '3 is a preferred embodiment of the arrangement; and Figs. 4, 5 and 6'sl10fw, modifications of the arrangement.

Figures 1 and 2 of the ,drawing'show the essential elements of my photo-electric cell in: one of its desirable forms. The evacuated cell envelope G contains the usual ,phmb sea Y sitive cathode K and an axial anode Aiii the form of a wire conductor. Fig; llshowsjtlie cell in longitudinal section; Fig; 211s: crosssectional View of the cell taken on the'line' 22 of Fig. 1 and'shows the slit or window W through which the light enters tlie cell.

In- ,tlie' embodiment of the inventionshowndiagrammatically in Fig. 30f tlieldrawing,

the cell contains the photo-sen'sitiy'e cathode K and an anodeA which-is of high resist ance, this high resistance beingindicatedin the drawingl b-y the diagrammatic; showing i l I V ,ofthe anode. A- battery,B"fis. connected 45 accelerat ngfield is strong enoughto-give an across the terminals of "tl1e anode 'A and;

the usual} battery and thelmetel G1 are connected between thecathodeand one ter- A the battery B furnishing the potential. There is exerted by an electron released from a particular point on the cathode a force determined by the resultant field of the charges distributed the length of the anode. If the beam from the light source is in the position 1? and falls upon the cathode at the point a, the accelerating force is determined approximately by the potential drop between the left end of the anode and a point 0 opposite the point a of the cathode. It,however, the incident light beam has the position P striking thecathode at the point I), the controlling potential drop will be that between the left end of the anode and a point (Z opposite the sensitized area of the cathode.

It is to be noted that the action of this form of cell is dependent upon a variation of E of the relation stated above.

The arrangement shown in Fig. 4 of the drawings is in eiiect the equivalent of the arrangement of Fig. 3 with the resistance of the anode increased to infinity. The cathode K is the same as the cathode K of Fig. 3. The anode A takes the form of a small sphere, preferably, and may be mounted substantially in the position shown in the drawings. It is to be understood, however, that the form and position of the anode may be varied to produce the desired relation to the cathode. The battery B and the meter Gr are connected between the electrodes as shown. The force exerted upon an electron released at any point on the cathode is a function of the distance between the anode and the cathode point of incidence. By a proper adjustment of the shape of the anode and the space relation with respect to the cathode, a direct relation between the displacement of an incident beam and the variation of the output current may be obtained. More specifically, it the incident light beam has the position P falling upon the cathode at the point e, the distance from the anode A to the point 0 determines the accelerating force. It the light beam takes the position P there is a large increase in the accelerating force, since the sensitized point f is now much nearer the anode.

The action of the cell of Fi 4 depends upon a variation of cl of the re ation stated above.

In the arrangement shown in Fig. 5 of the drawings, the anode A is of negligible resistance and the cathode K is made highly resistive, as indicated diagrammatically in this figure of the drawing. A battery B is connected between the anode and the terminal T of the cathode inseries with the meter G In this case again the point at which the light beam falls upon the cathode determines the strength of the accelerating field. The resultant potential between the anode and the cathode is that due to the battery B minus the potential drop from the cathode terminal drawings, the anode A is. of negligible resistance and the cathode K, is highly resistive,

as is the case with Fig. 5. The battery B" is connected across the terminals of the resistive cathode, and the battery 13,, and the meter G are connected, as shown, between the anode and one terminal of the cathode.

IVith this arrangement, the resultant poten.

tial is the algebraic sum of the voltage of battery 13., the potential drop from the left end of the cathode to the sensitized point upon which the light beam falls (the'battery B furnishing the voltage), and the potential drop due to the space current flowing along the cathode to the point of electron release. For instance, it the light beam is in the position P the resultant potential is the algebraic sum ofthe voltage of battery B.,,, the potential drop from the left-hand terminal of the cathode to the point 2', and the potential drop due to the space current flowing along the cathode to the point i; if the light beam takes the position P the resultant potential is the algebraic sum of the voltage of battery B the potential drop from the lefthand terminal of the cathode to the point j, and the potential drop due to the space current flowing along the cathode to the point 7'.

The action of the cell in the cases of Figs. 5 and 6 is dependent on a variation of E of the above-stated relation, as is thecase with the cell of Fig. 3.

It will help to clarify the operation of my cell it the arrangement shown in Figs. 3 and 6 are viewed as being essentially potentiometer circuits, the movable arm being adjusted by the deflection of the incident light beam and having in series with it a resistance equal to the internal resistance of the cell under the conditions of operation.

It is to be understood that the form of the evacuated cell or chamber and other structural details may be changed from the specific showing of the drawing and that such other changes as fall within the scope of the appended claims may be made without a departure from the spirit of the invention.

The arrangement shown in Fig. 4, the arrangement shown in Fig. 5 and the arrangement shown in Fig. 6 are disclosed and more specifically claimed in my co-pending applications filed as of even date herewith and numbered 134,299, 134,300, and 134,301, respectively. I

What is claimed is:

1. In a photo-electric device, an envelope,

a photosensitive cathode and an anode therein, the envelope being adapted to admit the whole of a beam of light to fall upon said cathode at different points over a substantial range of displacement of the beam, means for impressing a voltage between said cathode and said anode, and means for varying the output current of the device in response to the displacement of an incident light beam. 2. In a photo-electric device, an envelope,

a photo-sensitive cathode and an anode therein, the envelope being adapted to admit the whole of a beam of light to fall upon said cathode at different points over a substantial range of displacement of the beam, means for impressing a voltage between said cath ode and said anode, and means for varying the output current of the device in response to and in proportion to the displacement of an incident light beam of constant intensity.

3. In a photo-electric device, an envelope, a photo-sensitive cathode and an anode therein, the envelope being adapted to admit the whole of a beam of light to fall upon said cathode at diiierent points over a substantial range of displacement of the beam, means for impressing a voltage between said cathode and said anode, and means for varying the output current of the device in response to 3 variation in quantity of the incident light and also varying said current in response to the displacement of an incident light beam. 4.. In combination, a photo-electric cell comprising an envelope and a photo-sensitive cathode and an anode therein, said envelope being adapted to admit the whole of a beam of light to fall upon said cathode at diflerent points over a substantial range of displacement of the beam, means for impressing a voltage between said cathode and said anode, and means for varying the potential gradient in response to the displacement of an incident light beam.

5. In combination, a photo-electric cell comprising an envelope and a photo-sensitive cathode and an anode therein, said envelope being adapted to admit the Whole of a beam of light to fall upon said cathode at different points over a substantial range of displacement of the beam, means for impressing a voltage between said cathode and said anode, and means for varying the effective potential between said cathode and said anode in response to the displacement of an incident light beam.

In testimony whereof, I have signed my name to this specification this 4th day of September, 1926.

RALPH K. POTTER. 

